"Life starts all over again when it gets crisp in the fall."
(Scroll to the bottom for the answer.)
In the US, where I live, people often use fall to reflect, reset, and start fresh. In Japan, where I’m originally from, that feeling shows up in spring. I wonder if this has to do with when schools start.
Webinar series: Mastering CT: Advanced Techniques in Practice
The three-episode webinar series concluded this month. In case you missed them, here are the summaries and key takeaways.
Episode 1: High-attenuation Sample Imaging with X-ray Computed Tomography
This first session explored how to image dense, high-atomic-number, or large samples on a CT system. Typical examples include metals, concrete, and light but large parts. Dense materials are heavy-absorbing and can be challenging to image. Ted explained why these samples pose difficulties, including low material contrast, beam hardening, metal streaks, and sample-mount issues. He then walked us through a practical workflow for sample mounting, beam and filter selection, and data correction strategies to improve image quality.
Key takeaways:
Recognize the three common problems: low contrast, artifacts, and sample mounting issues.
Improve contrast by selecting a higher X-ray energy (higher voltage) so that more photons penetrate dense regions.
Mitigate artifacts by using appropriate filters (to “pre-harden” the beam), applying software corrections (beam-hardening correction), and choosing appropriate mounting so that dense zones don’t always block the X-ray beam path.
Mount smarter: orient the sample so denser features don’t continuously obstruct the beam during rotation. Odd-looking mounts often yield far better scans.
Think of the workflow as iterative: Mount → Set energy/filter → Scan → Post-process; then make adjustment → Scan again.
The second webinar focused on throughput and consistency: how to automate the CT workflow to run routine scans and analyses smoothly. Angela pointed out that automation wasn’t just about building a push-button script, and it is essential to reduce variability in results so that the data are reliable and comparable across samples and batches.
Key takeaways:
Consistency is often a neglected key to automation. If your scans of “identical” samples don’t show consistent X-ray analysis results, you have a problem.
Important steps to standardize include sample labelling (use embedded identifiers or photographs so samples don’t get mixed), sample mounting (stable, reproducible hold-downs), scan parameter templates (energy, filters, voxel size, FOV) defined for each sample size/composition.
In some cases, automation might not replace operator judgment, but it can reduce setup overhead, allowing the operator to focus on interpretation.
Fix as many factors as possible for reproducibility. For example, use custom holders, sample changers, and scripting in the reconstruction and image analysis.
Episode 3: 4D Structure Study with X‑ray Computed Tomography
The third webinar covered dynamic CT, also known as time-resolved 3D imaging or 4D CT, for studying how structures evolve or fail under various conditions. These conditions include mechanical loading, thermal cycling, or chemical exposure. Ted compared different approaches: cutting and destroying samples between the cycles, and imaging the object intact over time with 4D CT. The latter approach truly captures the “fourth dimension” (time) and links structural changes to performance or behaviors.
Key takeaways:
Traditional destructive techniques (cut/polish) are slow, invasive, and may introduce artifacts. Contrastingly, 4D CT enables in-situ, nondestructive monitoring of structural changes.
To set up a 4D experiment, you need an in-situ stage (load, temperature, environment), a CT system capable of repeating scans (or continuous/fast scans), consistent alignment, and a plan for linking structural change to behavioral data for analysis.
When analyzing data, start with capturing a baseline image, run the next scan (also trigger events, such as temperature change as required), reconstruct 3D volumes at each time-point, then segment/quantify changes (crack growth, porosity evolution, phase transformations) and correlate with external measurements (load, displacement, temperature).
When repeating CT scans, realistic sample size and geometry matter. If the sample is too large, resolution suffers; if too small, you might miss the structural change.
4D CT can reveal mechanisms (e.g., crack initiation, phase migration, structural collapse) that static scans cannot, giving crucial insight into reliability, durability, and degradation.
4D CT, also known as time-resolved CT or in-situ CT, is a powerful technique, but setting up experiments correctly to obtain useful data can be tricky. Here are the five keys to successful 4D CT setup:
1. Determine the balance between process duration and CT scan duration
Successful 4D measurements depend on balancing the process duration (how long the change takes) and the necessary duration of the CT scan.
The process duration needs to be longer than the total CT scan duration required to capture the event. If a process happens too fast (like a popcorn kernel popping in less than 0.1 seconds), standard 3D CT scanning may be impossible, and 2D projections might be necessary instead.
By knowing the total process time and the number of scans needed, you can calculate the maximum time available per CT scan.
2. Design and test the sample environment and in-situ setup
The environment must be carefully controlled (e.g., temperature, stress, humidity), which often requires using specialized in-situ chambers.
X-ray transparency: The chamber must have an X-ray transparent window so that X-rays can pass through to the detector. Components like compression stages, which are typically made of strong, dense materials (e.g., stainless steel), can be very absorbent of X-rays and block the signal, sometimes requiring the use of lighter-weight materials or spacers.
Cable and collision management: Since the sample and chamber often rotate, cables for power supply or signal control must be handled properly so they do not tangle, get pulled, or obstruct the X-rays or rotation.
Shielding: If you construct a custom stage (e.g., heating stage), the environmental control (like heat) must be shielded and limited only to the sample area to avoid damaging the CT scanner.
3. Manage the rate of change to prevent image blurring
Even if a process is slow enough to allow long scan times, the actual rate of change of the sample must dictate the scan speed.
If the sample changes its shape or internal structure significantly while being scanned, the resulting image will be blurred. For example, scanning rising bread dough for over four minutes might result in a blurred image, while an 18-second scan produces sharp detail.
To get a crisp image, you can do a fast scan so that the scan does not cover a large amount of change in the sample.
4. Validate image quality with test scans
Before starting a long, resource-intensive 4D experiment, you should run test scans and perform quick analyses.
This step ensures that the resulting image quality is sufficient to support the quantitative analysis planned for later.
5. Plan for data storage and analysis time
4D or in-situ CT scans can easily involve collecting 10, 20, or 30 scans, with each potentially being a large file (e.g., 10 gigabytes). They can quickly use up your data storage space.
It is crucial to consider the storage space and file size required to handle the data collected.
Adequate time and effort must also be budgeted for the subsequent analysis of this large volume of data. Make sure to use software that can handle a large amount of data and display the fourth dimension of time.
To learn more, watch the video from the "X-ray Computed Tomography for Materials & Life Science" series: 4D and In-situ Applications
Real Scientists, Not Actors
A collection of priceless and embarrassing moments curated by Sam Robles.
Francis Scott Key Fitzgerald
American novelist, essayist, and short story writer (24 September, 1896 – 21 December, 1940)
"Life starts all over again when it gets crisp in the fall."
That's a wrap. Please let us know how we can help you learn more about X-ray CT. We love to hear from you!
_Retouched.jpg?upscale=true&width=360&upscale=true&name=500px-F._Scott_Fitzgerald_(1921_portrait_-_crop)_Retouched.jpg)
